Use get_tenant_network in get_server_ip
Use get_tenant_network in get_server_ip

This is to use get_tenant_network to get ssh
network when CONF.validation.network_for_ssh is
not specified. Using get_tenant_network will be
more suitable here because when net_creds do not
have valid network attribute, it will look up
network according to CONF.compute.fixed_network_name.

Change-Id: Ifae1f64b74296b09d416c6f212d9914e25d8bec9

openstack/tempest,openstack/tempest,cisco-openstack/tempest,masayukig/tempest,masayukig/tempest,cisco-openstack/tempest